Plank theory revised (aka Materials Theory): First of all, it doesn't just work for planks, but it was introduced as a mean to increase one's planks stock, hence the original name

Second of all: it does not influence the harvesting pattern SIGNIFICANTLY. You may or may not see an increased amount of planks (or other materials) being harvested, but that is mostly regulated by what you are lacking. Whatever you are lacking and needing badly, in fact, will result to be more problematic to be harvested. But this is of secondary importance because:
the Theory influences more what you can see in the paper (which is the major source of materials in the first place). If you have large amounts of planks, you will most likely see more ads for planks of find concealed ones around crops.
This process works for barn, silo, mine materials and saws/axes. There is some belief it could also work with expansion items, but this has not been fully tested.
Sometimes having a lot of a particular material results in finding more of that from toolboxes too. For best results, apply the Plack Theory in conjunction with the Toolbox Tip.
This revision was necessary to avoid confusion about the harvesting and paper relationships